1871-] The Theory of Atmospheric Germs. 155 



upon them of living, growing, and multiplying organisms, 

 which, by their very acts of life and struggle for existence, 

 superinduce this disruption. The living beings which are 

 acknowledged to be present are the intimate causes and not 

 the adventitious signs, nor yet merely intermediate agents of 

 the decomposition of the material. 



If we investigate the question from the stand-point of the 

 second theory, we shall have to inquire concerning the living 

 organisms declared to be the prima moventia, how they are 

 brought into relation with the decomposable matters. The 

 close relation between the presence of atmospheric air and 

 the occurrence of the phenomena of putrefaction has been 

 constantly admitted. It is a matter of common knowledge 

 and common practice that to expel the air from a 

 putrescible substance is a powerful means of preserving it 

 from putrefaction. The presence of air is one of the condi- 

 tions insisted upon by the supporters of the theory of spon- 

 taneous generation as essential to the production of living 

 forms. No other gas can be substituted for atmospheric air 

 except oxygen. 



Upon what element of the air does its influence upon 

 putrefaction and upon the appearance of living forms 

 depend ? The nitrogen may be at once dismissed, as direct 

 experiment shows that it prevents putrefaction and is fatal 

 to living things. The influence might appear with greater 

 show of probability to be due to the oxygen. This was the 

 hypothesis of Gay-Lussac, but experience soon showed that 

 in many instances putrefaction was prevented when oxygen 

 had free access to putrescible solutions ; and when the pro- 

 gress of chemistry allowed Gay-Lussac's experiments to be 

 conducted with greater precision, it was found that in cases 

 wherein putrefaction was arrested by the attempted expul- 

 sion of air, oxygen, instead of being invariably absent from 

 the gaseous residuum, was very generally present. Further- 

 more, according to Dr. Bastian's late experiments, the de- 

 velopment of living forms may take place though all air may 

 have been excluded as rigidly as possible. 



Schwann concluded from his experiments that it is not 

 oxygen, at least the oxygen of the air, which occasions 

 putrefaction, but a principle contained in ordinary air which 

 heat can destroy. This same principle could also, according 

 to Schroeder and Dusch, be arrested by the meshes of 

 cotton-wool. And it could be arrested by flexures made in a 

 fine glass tube which admitted the air to a putrescible fluid, 

 according to observations made by Pasteur and more 

 lately repeated by Lister. Now, it may be urged that 



